Anatomical studies of Forsteronia G.Mey. (Apocynaceae) species of cerrado / Estudos anatomicos em especies de Forsteronia G.Mey. (Apocynaceae) de cerrado

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The leaf anatomy of four cerrado species of Forsteronia was investigated in order to determine characters that could help to identify individuals collected in vegetative stage. Eleven characters, two macromorphological and nine anatomical, were surveyed and are useful to differ F. australis from F. glabrescens and F. pubescens from F. thyrsoidea. Domatia and sessile and branched colleters were described for the first time in vegetative organs of species of Apocynaceae. The mucilage detection in the secretion of foliar colleters confirms the identification of these structures on the four species. The colleters are marginal or axilar, in agreement with the region of leaf primordia that they originate. In completely developed branches, the marginal colleters are deciduous and their traces are interpetiolar placed; the axilar colleters are persistent and they are placed upon the midrib, on the base of leaf blade. In all structural types (standard, sessile and branched), the secretion is produced by a secretory epidermis that surrounds the central core of parenchyma. The marginal colleters of F. glabrescens produce mucilage initially and become secretory of phenolic compounds on a second phase of secretion. The shoot apex histochemical analysis of F. glabrescents indicated that the secretory hypodermis produces a heterogeneous secretion containing fatty acids and phenolic compounds, while the latex is an emulsion of lipophilic substances including neutral lipids, fatty acids, phenolic compounds and alkaloids. Probably both the hypodermis and the laticifers protect the shoot apex from UV radiation and from herbivorous in the cerrado vegetation. The floral secretory structures found in F. australis, F. glabrescens, F. pubescens e F. velloziana were: idioblasts, hypodermis and epidermis, laticifers, style-head apical appendages and secretory epidermis; calycine colleters, bracteole colleters (only in F. pubescens); and nectaries. In F. glabrescens, the secretory idioblasts, the cells that constitute the style-head apical appendages, the hypodermis of several organs (anthers, corolla and calyx lobes, and ovary) and the nectary epidermis produce fatty acids and phenolic compouds. Three structural types of colleters (standard, sessile and branched) occur indefinitely distributed on the calyx base. The five nectaries may be free each other or united two and two (the fifth free), or an annular structure divided in five apical lobes. The gynostegium is a structure formed by the union of stamens and style-head; the last is surrounded by a palisade secretory epidermis. In F. glabrescens, the secretion is constituted by polysaccharides. The 5-lobed style-head has the five projecting ribs adnated to the connective by the cementation of the both structures epidermal cells walls. The glue zone is divided in two functional and structural parts, one of them involved in production and storage of secretion, and other involved with the adnation process. These gynostegium characters, associated to occurrence of sessile calycine colleters, support the exclusion of the genus from the tribe Apocyneae and their inclusion in Mesechiteae.

ASSUNTO(S)

leaves forsteronia ginostegio apocynaceae histochemistry folhas - anatomia forsteronia apocinaceas histoquimica gynostegium

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